“The senses deceive from time to time, and it is prudent never to trust wholly those who have deceived us even once.” –Rene Descartes

Happy New Year, everyone! While many of you are still awestruck at the image of the Universe compressed into a single year, it’s time to move forward to the next thing. For those of you new to the game, as is tradition around here, every weekend I come to you with some music you may not have heard before and some important, fun, interesting, or educational thing to amuse you.

But as far as your eyes go, I’ve got a fun little trick to show you. Take a look at the object below; I’m sure it’s one you’re all familiar with.

Image credit: Unknown; retrieved from Will Sommer's blog.

The famed Leaning Tower of Pisa, of course. But what I’m going to show you now are two shots of the Leaning Tower, side by side, and you’re going to tell me which image shows a more slanted tower: the left or the right?

Images credit: Calum Davidson.

If I told you that the image on the left was from after the restoration, where the tower had been leveled out some, and the image on the right was from before, where the lean was more severe, you’d probably find that explanation pretty reasonable.

But that is not true!

These two images are actually identical to one another, and it is only your perception that leads you to believe that the one on the right is leaning more severely than the one on the left. Don’t believe me? Take a look at the same image, repeated 5 times in a row horizontally, below.

If you want even stronger evidence, view the larger version on as large a screen as possible!

Surely it appears to you that the tower furthest to the right slants most strongly to the right, while the leftmost one is nearly perfectly upright. Want to do something fun? Fill your screen with the image and move your head so that you are aligned with the rightmost tower, and look at how nearly perfectly vertical the one on the left looks. Now move your head to the left so that it’s aligned with the leftmost tower, and the one on the right should have such a severe slant that it’s inconceivable the tower in that picture hasn’t fallen yet!

And yet, it’s all the same image. What’s going on, of course, is an optical illusion.

Image credit: Mighty Optical Illusions / Larry from Michigan.

Remember how easily your perceptions can fool you! Despite what you think your eyes are telling you, you can only see things relative to the other things you’re looking at. It’s well-known that this is true for color, but most people don’t realize that it’s true for shape and slant as well!

I’ll do my best to keep on top of when things are different from how they appear, from the optical to the abstract, and I hope you all can do the same. In the meantime, Happy New Year, and I wish you all a great start to your 2012!

I failed this test too. I just looked at the position of the top & bottom & saw that they were the same distance from the edge in both pics. And that all the details; clouds, flags, etc were identical.

One of the hot topics in neural research these days is not how neurons activate each other, but the converse: How they inhibit each other. Turns out that such inhibitory effects are deeply involved with many of the more perplexing images, including the appearance of slants where there are none.

The illusion definitely depends on you focusing on the towers first. Like several other posters above, I looked at background elements (assuming that the tilt would be relative to the buildings behind the tower) and concluded that the two images were identical. But if I intentionally look at the towers and exclude the background, I can “see” the illusion Evan discusses.